The purpose of this study is to see if a new drug called nevirapine (NVP) is safe when given to HIV-infected pregnant women in active labor, and, in some cases, to their babies. This study will also look at the levels of nevirapine in the blood of HIV-infected pregnant women and their babies. Part of this study will also see if nevirapine is present in breast milk when given to HIV-infected pregnant women in active labor. This information may be useful in treating mothers in other countries who routinely breastfeed their babies, despite HIV+.